Polyoxyethylene (20) sorbitan monooleate, or POE 20S, is one of palm-based surfactants commonly used as adjuvant in pesticide formulation. Toxicity study of POE 20S toward plants is still lacking since public is usually misinformed that adjuvant is non-toxic. Therefore, a study was conducted to investigate the effect of POE 20S on terrestrial plants, i.e., tomato and corn. At every one-week interval, aqueous solutions of POE 20S at 1%, 3%, 5%, 7% and 10% w/v were sprayed onto planted seeds. Germination time, number of seedlings survived, shoot length, shoot weight and visual symptoms of injury were determined and compared with control. The results showed that the first spray of all POE 20S concentrations did not inhibit the germination of both tomato and corn seeds. All seeds germinated and emerged. However, the next 10% spray treatment of POE 20S showed significantly lower survival in both plants due to necrosis and severe shrivelling of their leaves. In terms of germination time, shoot length and shoot weight, only tomato plants showed no significant differences between all concentrations tested and the control. We concluded that POE 20S is safe and not harmful to non-target terrestrial plants if appropriate dilution is used for pesticide formulation.